ET Junk

From Discovery.com:
As powerful space telescopes seek out Earth-like planets, and SETI radio telescopes listen for transmissions from aliens, physical evidence for intelligent extraterrestrials might be right in our backyard.

I'm not talking about flying saucers or oddball ancient artifacts attributed to visits by so-called "space gods," however. Instead, I'm looking for something as mundane as the pieces of interstellar probes that could have visited our solar system on numerous occasions over geologic time.

If technological extraterrestrial civilizations are common in our galaxy, then they should have the wherewithal and curiosity to send robotic probes to other star systems. We already have five star-bound spacecraft destined to roam the galaxy forever: two Pioneer probes, a pair of Voyagers, and the New Horizons craft now speeding toward Pluto.

The aliens' motivations may be the same as ours; if we found an Earth-like world nearby, there would be an inevitable desire to send an unmanned craft to see what kinds of creatures are living there. We'd have a burning curiosity to behold how the power of biological evolution has played out among the stars.

Looking for alien "calling cards" in the solar system is not a new idea. It has been popularized in numerous science fiction stories and movies. In Arthur C. Clarke's 1951 short story The Sentinel, astronauts come upon an alien-built pyramid on the moon that remains inscrutable.

A recent paper by Jacob Haqq-Misra and Ravi Kumar Kopparapu of Pennsylvania State University takes a new look at this twist on the Fermi Paradox: "Where Are They?"

The authors propose that an alien probe may be as small as a car, but no bigger than a modest-sized house.

Certainly, for the propulsion demands of interstellar travel the less massive -- hence smaller -- the payload, the better. But finding it among our planets would be as difficult as finding a needle on a football field covered in three feet of hay, say the authors.

The researchers developed an equation that can be applied to a portion of the volume of the solar system and determine whether sufficient searching has been done to rule out any E.T. souvenirs.

They conclude: "Extraterrestrial artifacts may exist in the solar system without our knowledge simply because we have not yet searched sufficiently. The vastness of space implies that it will take some time before every nearby object can be considered devoid of (space probes)."

We are just beginning to take close-up look at other planets with enough sharpness to see small artifacts, if they are there...

A Solar System Littered With Alien Artifacts?
Ray Villard
Wed Nov 9, 2011
http://news.discovery.com/space/our-solar-system-might-be-littered-with-alien-artifacts-111109.html